This invention relates generally to arc welding, and more particuarly to a new and improved contact tip for use in an arc welding gun for guiding and supplying current to a consumable wire electrode.
In a conventional metal inert gas (MIG) arc welding process, a continuous length of welding filler wire is fed from a spool or a roll to an arc welding gun, where it passes through a contact tip which guides the wire to a welding zone and supplies the current necessary to maintain an arc between the wire extending from the tip and a workpiece. The wire, which is continuously fed through the contact tip during welding, constitutes a consumable electrode which is fused down in the electric arc. The welding gun also supplies inert gas to the welding zone which envelopes the arc in an inert gaseous atmosphere.
Conventional contact tips typically comprise a short length of guide tube formed of a good electrical conductor, such as copper, disposed coaxially within a cylindrical gas cup or nozzle in the head assembly of the welding gun. The tip may be tapered toward its outlet end, and may be connected to the head assembly by screw threads or by frictional engagement with a tip receiving device within the head assembly. The inner diameter of the guide tube, i.e., tip bore, is sized to afford sliding contact with the welding wire passing therethrough to enable electrical current to be supplied to the welding wire.
Contact tips operate under very severe conditions and wear out very rapidly. Typically they have a life of only several hours of use. Being close to the electrical arc, they are subjected to very high temperatures which may cause warping of the tip or fusion of the tip and the welding wire. Oxidation and the condensation of metal vapors causes fouling of the tip and a build-up of scale. Moreover, the rate at which welding wire is fed through typical arc welders may be of the order of 1000 feet per minute. Abrasion between the tip, which is typically copper, and the welding wire, which is typically steel, tends to cause enlargement of the tip bore and impairment of the electrical contact between the tip and the welding wire. The build-up of oxidized metal particles and scaling within the tip bore can also produce resistance heating of the tip which can further promote fusion and blockage of the tip bore, and render it unusable. As a result, contact tips in arc welders must be replaced quite frequently, which is both expensive and time consuming.
It is desirable to provide contact tips for arc welders which avoid such problems, and it is to this end that the present invention is directed.